Are any of his business ideas seeming worthwhile / is he passionate and dedicated to any of them? Or just jumping from one thing to the next?
I was in a similar situation about 2 years ago - if useful, here's how it played out for us (me + partner, + DD5)..
Partner lost well paid job as senior developer through redundancy. Job market was abysmal, job hunting amd constant ghosting/rejection was making him v depressed. To keep the depression at bay he started 'showing up' to work each day (our home office) to work on projects or business ideas he had. One really started to hold his attention, and he was taking it really seriously.
Throughout this time we both instigated discussions about finances, how long my salary + savings would last, whether he could stop job hunting and dedicate time to the business idea instead, how much i could help with said business idea, whether i could increase my work hours, what expensises we'd be willing to cut, how much of our savings we were willing to burn through etc etc etc. These were not always the easiest conversations but we were always well aware of how long we had before it was crunch time and he needed to get a job (any job) again.
He took out a business loan and built a software product and launched his business. He took a minimum wage from the business loan. He took odd jobs gardening for extra cash. He attended networking events several times a week, he worked during evening and some nights and weekends so we could cut down on childcare costs. He really put a lot into the business.
3 months ago we came to the crunch point! After a year, the business loan had run out. He only had two companies paying for his software. He started applying for jobs again, both in software and ANYTHING else he could think of, bar work, factory assembly lines, anything that would get us through money wise.
Luckily he got a software job. His business is on pause.
It'll take another 6 months for our savings to recover. More than that to pay off the business loan.
In all of our discussions, the changes to our previous plans were always talked about. It meant no longer moving abroad as we had planned, it meant a change to full time for me (which was never the plan while my daughter was young). The pay-offs were always discussed. The length of time I was willing to scrimp and scrape was made clear.
It was a risk we went into together. It has led to opportunities and work, though the business itself hasn't worked out (yet?).
Now he's working again we've discussed reducing my hours again. We've re-evaluated moving abroad.
I guess my point in relaying what happened for us is that its something we went into together. We both sacrificed some of the things we wanted in order to take a risk and have him try at this business for a year. He understood the limit of what we could do financially and how long I was willing to support for, and we're continuing to evaluate our goals and adjust towards those now.
Obviously you'll have different goals and priorities and finances so I recommend a good honest discussion about what you're willing to risk/put on pause while he pursues a business idea, how much support you're willing/able to give, and when the cut off on that support needs to be!